The present invention relates to a process for eradicating or controlling pests, respectively for protecting or preserving stored commodities, in particular bulk commodities such as agricultural produce, e.g. grain, against deterioration by pest action, comprising the introduction into and maintenance in the commodity in a substantially gas-tight enclosure of a pesticidal atmosphere comprising carbon dioxide.
It is known hat carbon dioxide above certain concentrations is toxic to pests, e.g. insects such as occur in agricultural commodities, e.g. grain. Experiments to eradicate or control pests or for protecting or preserving stored commodities, in particular bulk commodities such as agricultural produce and processed or semi-processed foodstuffs or animal feeds against deterioration by a pest action using carbon dioxide or mixtures of carbon dioxide with other either inert or pesticidal gases have been conducted in various countries. These experiments have been successful to some extent on a laboratory scale, however, various difficulties have been experienced in attempts to apply such procedures economically on a large scale.
Bulk commodities in which pests are traditionally controlled by fumigation include all kinds of grain and grain products, legumes, e.g. beans, soya beans and peas, nuts, ground nuts, cocoa beans, coffee, tobacco, but also non-edible commodities such as cotton, wool, sisal. The pests which one wishes to eradicate to control, besides higher animals such as rodents, e.g. rats and mice, include in particular a variety of insects such as bugs, weevils, moths, cockroaches as well as their eggs and larvae. The pest control procedures are applied to the commodities, when packed in bags, bales or in like containers, but also when in loose bulk form in various kinds of storage or transport facilities, including bulk storage sheds, silos, open-air plastic lined and covered dumps, railway trucks, containers and shipholds.
Traditional fumigants included methyl bromide, hydrogen cyanide, ethylene dibromide and ethylene oxide which are highly toxic and very dangerous to humans. Accordingly, alternative fumigants, in particular hydrogen phosphide, normally released at or inside the fumigation site from hydrolysable metal phosphide compositions have become far more acceptable. Phosphine leaves no residues and does not accumulate in the environment or in any parts of the biological food chain. Nevertheless, for short term environmental reasons, e.g. smell, or where there is a risk of leakage of gas into spaces occupied by humans, or where it is necessary to handle commodities immediately after treatment and before the phosphine gas has had time to dissipate, it is sometimes desirable to employ a fumigant having less toxicity than hydrogen phosphide. In such conditions particularly, the use of carbon dioxide as a fumigant would be highly desirable. To date the variations existing in the construction of commodity stores and their frequent lack of gas tightness which often can be overcome only at great cost, have militated against the commercially successful fumigation with carbon dioxide on a large scale. The technical success of carbon dioxide fumigation is dependent on the concentration of carbon dioxide maintained in the space to be fumigated and the ability to maintain such concentrations (which are very high) for the required length of time. It has been previously known (DE-OS 25 56 999) to fumigate bulk commodities, separated from the atmosphere by being covered and sealed off by a gas-tight foil. According to that prior art, relatively small containers filled with a gas or liquefied gas were set up underneath the foil and opened by special devices in order to release the required small volumes of highly poisonous gas to the enclosed space. That procedure is not suitable for the employment of carbon dioxide as a fumigating gas, because of the high concentration in which such carbon dioxides has to be employed, involving the application of large volumes to achieve the required concentration at which carbon dioxide is reliably pesticidal. It is also known (DE-PS 869 135) to introduce highly toxic fumigation gases such as cyanic acid or ethylene oxide through pipe systems equipped with nozzles and valve from the outside into spaces to be fumigated. That process as well is suitable only for the fumigation of closed spaces with gases of high toxicity which are introduced into the space in relatively small quantities. In order to be able to monitor in that context the maintenance of the desired, relatively low concentration of such highly toxic gases in a space to be fumigated and to automatically maintain the desired concentrations a monitoring and control system is disclosed in DE-PS 32 25 515.